She found an abandoned baby and wants her daughters to breastfeed him so that he will become a mahram for her

A neighbor of ours found a few hours old baby. She fears for him from the mistreatment of the orphanages. She wants to bring him up, but when he grows up it will be haram if he stays with her alone in the house. She says that if she brings him up like she does with her own children, she will not able to leave him. She has married daughters and they have babies. Shall she ask her daughters to breastfeed this baby so that she becomes his grandmother through breast feeding? And so it will not be haram if he stays with her at home. Or this will be considered a disliked trick? 
My mother has breastfed a daughter of our neighbor with my older brother several times. So she became a sister of my brother (of breastfeeding). Has she and her sisters become sisters for me as well or sisters for my brother who was breastfed with her only? This question is to specify the limits of my dealings with them, are they considered my sisters, or strange women to me?.